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MEMS Piezoresistive Pressure Sensor: a Survey Shwetha Meti et.al. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 4, (Part - 1) April 2016, pp.23-31 RESEARCH ARTICLE OPEN ACCESS MEMS Piezoresistive Pressure Sensor: A Survey Shwetha Meti*, Kirankumar B. Balavald*, B. G. Sheeparmatti* *(Department of Electronics and Communication, Basaveshwar Engineering College, Bagalkot-587102 ABSTRACT Piezoresistive pressure sensors are one of the very first products of MEMS technology, and are used in various fields like automotive industries, aerospace, biomedical applications, and household appliances. Amongst various transduction principles of pressure sensor piezoresistive transduction mechanism is widely used. Over a decade therehas been tremendous improvement in the development of the design of piezoresistive pressure sensor starting with the invention of piezoresistance in the silicon to the recent piezoresistive pressure sensor materials. Because of its high sensitivity, high gauge factor, independent to the temperature, linear operation over a wide range of pressure, and many more advantages. This paper provides survey of piezoresistive pressure sensor including their pressure sensing mechanism, evolution, materials, design considerations, performance parameter that to be considered and the fabrication process used Keywords-MEMS, Pressure sensor, Piezoresistor, Silicon material. Common methods that uses piezoresistive I. INTRODUCTION technologies are Silicon (Mono crystalline), In conjunction with temperature, pressure Polysilicon Thin Film, Bonded Metal Foil. 1.7 is one of the major physical quantities in our Capacitive pressure sensor uses a diaphragm and environment. A pressure sensor often acts as a pressure cavity to create a variable capacitor to transducer; it produces a signal as a function of the detect strain due to applied pressure, capacitance pressure imposed. MEMS pressure sensors are decreasing as pressure deforms the diaphragm. covering foremost part of the sensor market in 1.8Resonant pressure sensor uses the changes contemporary years and are fast developing with in resonant frequency in a sensing mechanism to brand new capabilities. Pressure sensors are used in measure stress, or changes in gas density, caused many applications like aerodynamics, biophysics, by applied pressure. automobile, safeguards and many more domestic Many MEMS instruments were applications. Various types of pressure sensors can manufactured and commercialized from several be categorized based on the sensing mechanisms years and have reached consumer. The present they are. 1.1 Absolute pressure sensor measures pressure sensors going through many challenges static, dynamic or whole pressure with reference to that has to be used in the application like high a vacuum. 1.2 Gauge pressure sensor calculates the pressure. Temperature is a main factor in the pressure relative to atmospheric pressure. When it efficiency of MEMS pressure sensor, were these shows zero, then the pressure it is measuring is have to be used in many applications like aerospace same as the ambient pressure. 1.3 Relative pressure utility and harsh environment. Consequently, for sensor measures static, dynamic or total pressure this kind of environment special sensing devices with regards to the ambient pressure. 1.4 Optical are requiring to adapt a high temperature and high pressure sensor techniques include the use of pressure environment. Among all the various type anphysical change in the optical fiber to detect the of MEMS pressure sensor piezoresistive pressure strain due to an applied pressure. This technology sensors are widely used, because these sensors is employed in many challenging applications provides a high sensitivity and it allows a linear where the measurement may be highly remote, operation over a wide range of pressure. under high temperature, or may benefit from Piezoresistive pressure sensors are one of the very applied sciences inherently immune to first products of MEMs technology. Those products electromagnetic interference. 1.5 Differential are broadly used in biomedical applications, pressure sensor measures the difference between automotive enterprises and household appliances. two pressures, one connected with each side of the The piezoresistive pressure sensor have mainly sensor. Differential pressure sensors are used to been studied and commercialized because of their measure many properties like pressure drops high yield and wide dynamic range. A silicon based through oil filters or air filters, fluid levels or flow pressure sensor is one of the major applications of rates. 1.6 Piezoresistive pressure sensor uses the piezoresistive sensor. Recently MEMS situated the piezoresistive effect of bonded strain gauges to technologies includes silicon (Si), silicon on detect the strain due to an applied pressure, insulator (SOI), silicon on sapphire (SOS), silicon resistance increasing as pressure deforms the carbide (SiC), steel, carbon nanotubes (CNT) and www.ijera.com 23|P a g e Shwetha Meti et.al. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 4, (Part - 1) April 2016, pp.23-31 diamond had been observed to be in a position to doping concentrations are increased further [14, 15- furnish the critical ruggedness to be capable to 17]. Based on this phenomenon, the existing adapt and provide the better performance in harsh piezoresistive theories of Polysilicon were environment. This paper focus on the survey of established during 1980s~1990s and used to predict MEMS based piezoresistive pressure sensor, the process steps for the optimization of device current trends involved in development of performance. piezoresistive pressure sensor and their outlook. Later years carbon nanotubes have drawn Section II explains about the evolutions of much attention since their discovery in 1991 piezoresistive pressure sensor. Principle and because of their unique electronic and mechanical sensing mechanism of piezoresistive pressure properties. In 1991, multi-walled nanotubes were sensor is explained in section III. Section IV is first discovered by Ijima by arc-discharge about the materials that are used in the design of technique when he saw fine threads in a bit of shoot diaphragm and their properties. Section V and VI under electron microscope. The strands were very discuss about the performance parameter and the thin and long tubes of pure carbon. SWNTs were design consideration of the piezoresistive pressure synthesized for the first time by Ijima and Ichihashi sensor. The fabrication of the piezoresistive [18] and Bethune et al. [19] in 1993 using metal pressure sensor is discussed in section VII. catalyst in arc-discharge method. Laser-ablation technique was used by Thess et al. [20] in 1996 to II. EVALUTION OF PIEZORESISTIVE produce bundles of aligned SWNTs. For the first PRESSURE SENSOR time, catalytic growth of MWNTs by CVD was Ever since the discovery of proposed by Yacaman et al. [21]. Liu [22] and Dai Piezoresistance in silicon by C.S.Smith in1954 [1] [23] demonstrated that piezoresistive pressure silicon based micro pressure sensors have been sensors can be realized with CNTs. They grew extensively studied over the past three decades. SWNTs on suspended square polysilicon Pfann and Thurston [2] were among the first to membranes. When uniform air pressure was realize a working of MEMS based pressure sensor applied on the membranes, a change in resistance designed using two longitudinal and two transverse in the SWNTs was observed. Moreover, the diffused piezoresistors in the Whetstone's bridge membrane was restored to its original condition for better sensitivity. Kanda [3] in his work has when the gas was pumped out, indicating that the presented a model which enables the calculation of process is reversible. Dharap et al.[24] argued that piezoresistive coefficients as a function of doping the conventional sensors have disadvantage that concentration and temperature. Enhancing the they are discrete point, fixed directional, and are sensitivity has also been a main issue in the not embedded at the material level. To overcome research of micro pressure sensors. Design these limitations, they developed a CNT film modifications like employing a bossed diaphragm sensor for strain sensing on macro scale. The and multiple diaphragms [4, 5] and material sensor was based on the principle that the modification by using phosphorous diffused electronic properties of CNTs change when polysilicon piezoresistors [6] polymer diaphragms subjected to strains. In recent years high and alternate piezoresistive materials [7-10] have temperature pressure sensor is one of the hot also been studied. The other technology can be research topics in the industry. Because of the brought to solve the isolation problem of devices special environments they are used in, the and substrates, but increases the fabrication cost requirements for the design and manufacture of the greatly. The discovery of piezoresistive effect in sensor are very strict. It is important to research polysilicon in the 1970s [11] facilitates its high temperature pressure sensors for every walk of applications for sensing devices [12, 13]. As for life [25, 26]. So Silicon carbide (SiC) has been polysilicon, the p-n junction isolation is avoided, so recognized as an appropriatesemiconductor that the devices can work at higher temperatures. material for harsh environments such asspace Moreover, polysilicon based devices have the applications and
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